1. Field of the Invention
The present invention relates to a chip package and a method for fabricating the same. More particularly, the present invention relates to a chip package having two different kinds of metal pads over a same semiconductor substrate and a method for forming the same.
2. Brief Description of the Related Art
At present, the market for multimedia applications is expanding rapidly. The integrated circuit (IC) packaging techniques, therefore, also need to be able to accommodate the developing trends of electronic devices, such as, digitalization, networking, localization, and user friendliness. In order to meet the above requirements, electronic devices must be multifunctional, highly integrated, miniaturized and light weighted, inexpensive, and must provide a high operating speed. High-density packages, such as, ball grid arrays (BGAs), chip scale packages (CSPs), flip chips, and multi-chip modules (MCMs) thereby have been developed. For high-density IC packaging, the speed of signal transmission increases as the wiring length decreases. Thus, the application of bumps has become the main trend in high-density packaging.
Further, in this packaging structure, solder bumps are used as a medium for electrical connections of a semiconductor chip to another one. Besides, multiple wires formed by a wirebonding process connect the semiconductor chip to a printed circuit board.
Conventionally, a majority of the bonding pads on a semiconductor wafer is formed of aluminum. If solder bumps and wirebonds are to be formed on a same chip, some damage to original aluminum pad could easily occur when an under bump metallurgy (UBM) layer acting with an adhesion function and a barrier function is formed on the original pads for solder bumps. The under bump metallurgy layer is etched by hydrofluoric acid (HF), which leads the aluminum pads for being wirebonded thereto to be damaged by the etchant of hydrofluoric acid (HF).